Rigid wave pattern design on chip carrier substrate and printed circuit board for semiconductor and electronic sub-system packaging

ABSTRACT

A rigid wave pattern formed on a first side of a substrate in a semiconductor die package. The rigid wave pattern aligns with and overlies the contact fingers formed on the second side of the substrate. When the substrate and dice are encased during the molding process, the rigid wave pattern effectively reduces deformation of and stresses on the dice, therefore substantially alleviating die cracking.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the present invention relate to a method of forming achip carrier substrate to alleviate chip cracking, and a chip carrierformed thereby.

2. Description of the Related Art

The strong growth in demand for portable consumer electronics is drivingthe need for high-capacity storage devices. Non-volatile semiconductormemory devices, such as flash memory storage cards, are becoming widelyused to meet the ever-growing demands on digital information storage andexchange. Their portability, versatility and rugged design, along withtheir high reliability and large capacity, have made such memory devicesideal for use in a wide variety of electronic devices, including forexample digital cameras, digital music players, video game consoles,PDAs and cellular telephones.

While a wide variety of packaging configurations are known, flash memorystorage cards may in general be fabricated as system-in-a-package (SiP)or multichip modules (MCM), where a plurality of dice are mounted on asubstrate. The substrate may in general include a rigid base having aconductive layer etched on one or both sides. Electrical connections areformed between the dice and the conductive layer(s), and the conductivelayer(s) provide an electric lead structure for integration of the diceinto an electronic system. Once electrical connections between the diceand substrate are made, the assembly is then typically encased in amolding compound to provide a protective package.

In view of the small form factor requirements, as well as the fact thatflash memory cards need to be removable and not permanently attached toa printed circuit board, such cards are often built of a land grid array(LGA) package. In an LGA package, the semiconductor dice is electricallyconnected to exposed contact fingers formed on a lower surface of thepackage. External electrical connection with other electronic componentson a host printed circuit board is accomplished by bringing the contactfingers into pressure contact with complementary electrical pads on theprinted circuit board. LGA packages are ideal for flash memory cards inthat they have a smaller profile and lower inductance than pin gridarray (PGA) and ball grid array (BGA) packages.

A cross-section of a conventional LGA package is shown in FIG. 1. One ormore die 20 are mounted on a substrate 22 via die attach 24. Thesubstrate 22 in general is formed of a rigid core 26, of for examplepolyimide laminate. Thin film copper layers 28 may be formed on the corein a desired electrical lead pattern, including exposed surfaces for thecontact fingers, using known photolithography and etching processes. Thecontact fingers 30 may be formed of a layer of gold deposited on thecopper layer 28 to provide the electrical connection of the package tothe host PCB. The dice may be electrically connected to the substrate bywire bonds 32. Vias (not shown) are formed through the substrate toallow electrical connection of the dice through the substrate to thecontact fingers 30. The substrate may then be coated with a solder mask34, leaving the contact fingers 30 exposed, to insulate and protect theelectrical lead pattern form on the substrate. Further examples oftypical LGA packages are disclosed in U.S. Pat. Nos. 4,684,184,5,199,889 and 5,232,372, which patents are incorporated by referenceherein in their entirety.

Referring now to FIG. 2, after the dice is mounted onto the substrate,the assembly is packaged within a molding compound 40 to protect theassembly. During the molding process, the molding machine may output aninjection force typically about 0.8 tons to drive the molding compoundinto the mold cavity. For dice having a footprint of about 4.5 mm by 2.5mm, this injection force may result in a pressure down on the dice ofabout 1.2 kgf/mm².

The bottom surface of an LGA package is typically not flat. As shown inFIGS. 1 and 2, the fingers 30 are recessed within the package, above theplane defined by the solder mask 34. The flush position of the soldermask results in an equal and opposite force pushing upward on thesubstrate, against the force of the mold compound, at positions beneaththe lower surface solder mask. However, as the contact fingers are notflush with the lower surface of the solder mask, there is no equal andopposite force at positions beneath the contact fingers. This results instress buildup within the dice at positions in the dice located over thecontact fingers.

In the past, semiconductor die were better able to withstand the stressgenerated during the molding process in LGA packages. However, chipscale packages (CSP) and the constant drive toward smaller form factorpackages require very thin dice. It is presently known to employ waferbackgrind during the semiconductor fabrication process to thin dice to arange of about 8 mils to 20 mils. At these thicknesses, the dice areoften not able to withstand the stresses generated during the moldingprocess, and the dice deform under the molding pressure (as shown by thedashed lines in FIG. 2).

Deformation of the dice over the contact fingers can cause fractures inthe dice, known as die cracking, such as the die crack 50 shown in FIG.2. Die cracking under the stress of the molding process will generallyresult in the package having to be discarded. Occurring at the end ofthe semiconductor fabrication and packaging process, this is anespecially costly and burdensome problem.

The problem of die cracking has not previously been addressed by thechip carrier substrates. The area on the top side of the substrate,above the contact fingers on the bottom side of the substrate, generallyinclude layer 28 of copper, etched for example in a mesh pattern asshown in prior art FIG. 3. It is also known to provide a solid uniformlayer of copper above the contact fingers as shown in prior art FIG. 4.However, owing to differences in thermal expansion coefficients, a soliduniform layer of copper on the substrates leads to warping and otherproblems during the elevated temperature processes during packageformation. Moreover, with thin semiconductor die, die cracking occurs atunacceptably high rates during the molding process with either one ofthe patterns shown in FIGS. 3 and 4.

SUMMARY OF THE INVENTION

One embodiment of the invention relates to a strengthened semiconductordie package. The semiconductor die package is formed of one or moresemiconductor die mounted on a substrate, and a molding compound forencapsulating the one or more semiconductor die and substrate. Thesubstrate includes first and second conductive layers, in one or both ofwhich are formed electrical conductance patterns. A portion of theconductance pattern on a first of the conductive layers is formed intocontact fingers for electrical connection of the die package to externalcomponents. The second conductive layer includes a pattern, referred toherein as a rigid wave pattern, for reducing deformation and stress onthe one or more die otherwise resulting from the contact fingers duringthe molding process.

In embodiments of the invention, the rigid wave pattern is formed in afirst surface of the substrate to align with and overlie the contactfingers formed on the opposite surface of the substrate. The rigid wavepattern may include etched portions and an unetched portion surroundingthe etched portions. There may be one etched portion for each contactfinger, and each etched portion is approximately the same size as itscorresponding contact finger in the opposite surface of the substrate.

In an embodiment of the present invention, each of the etched portionsmay have four distinct sections, which together form a portion of anellipse, truncated at the top and bottom, and separated at its middlebetween the top and bottom. The unetched portion surrounding the etchedportions may be generally rectangular in shape and devoid of etching.The shape of the etched and unetched portions of the rigid wave patternmay vary in alternative embodiments.

With the one or more die overlying some or all of the contact fingerswhen mounted on the substrate, the rigid wave pattern according toembodiments of the present invention effectively reduces deformation ofand stresses on the individual dice, therefore substantially alleviatingdie cracking. Moreover, the etched portions of rigid wave pattern may beformed at the same time and in the same process as the electricalconductance patterns on the substrate. Thus, the advantages provided bythe present invention may be achieved without any additional processingsteps or any additional fabrication costs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a prior art cross-sectional view of a dice mounted on asubstrate in a LGA package.

FIG. 2 is a prior art cross-sectional view of the packaged dice andsubstrate, where the die have cracked as a result of pressure during themolding process.

FIG. 3 is a prior art top view of an un-etched copper layer formed onthe upper surface of a conventional chip carrier substrate.

FIG. 4 is a prior art top view of a mesh-patterned copper layer formedon the upper surface of a conventional chip carrier substrate.

FIG. 5 is a top view of a chip carrier substrate, looking through thetop surface to the contact fingers on the bottom surface (the contactfingers on the bottom surface being shown in phantom).

FIG. 6 is a top view of a chip carrier substrate, the top surfaceincluding a rigid wave pattern according to embodiments of the presentinvention.

FIG. 7 is a cross-sectional view through line 7-7 in FIG. 6.

FIG. 8 is a cross-sectional view through line 8-8 in FIG. 6.

FIG. 9 is an enlarged top view of a portion of a rigid wave patternaccording to embodiments of the present invention.

FIGS. 10-13 are top views of a chip carrier substrate, the top surfaceincluding rigid wave patterns according to alternative embodiment of thepresent invention.

FIG. 14 is an enlarged top view of a portion of a chip carriersubstrate, the top surface including a rigid wave pattern as shown inFIG. 13.

FIG. 15 is a top view of a chip carrier substrate, the top surfaceincluding a conductance pattern and a rigid wave pattern according toembodiments of the present invention.

FIG. 16 is a side cross-sectional view of a semiconductor packageincluding a dice and a chip carrier substrate having a rigid wavepattern according to an embodiment of the present invention.

FIG. 17 is a flowchart of a process for forming a rigid wave pattern ona substrate according to the present invention.

FIG. 18 is a flow chart illustrating the manufacturing process of a chipcarrier substrate according to the present invention.

DETAILED DESCRIPTION

Embodiments of the invention will now be described with reference toFIGS. 5 through 18, which relate to a strengthened semiconductorpackage. It is understood that the present invention may be embodied inmany different forms and should not be construed as being limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete and will fully conveythe invention to those skilled in the art. Indeed, the invention isintended to cover alternatives, modifications and equivalents of theseembodiments, which are included within the scope and spirit of theinvention as defined by the appended claims. Furthermore, in thefollowing detailed description of the present invention, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present invention. However, it will be clear tothose of ordinary skill in the art that the present invention may bepracticed without such specific details.

FIGS. 5 and 6 are top views of a portion of a chip carrier substrate100, and FIGS. 7 and 8 are cross-sectional views through differentplanes normal to the top and bottom surfaces of the substrate 100. Asseen in FIGS. 7 and 8, the substrate 100 may have a top surface 102 anda bottom surface 104. Substrate 100 may be formed of a core 106, havinga top conductive layer 108 formed on a top surface of the core, and abottom conductive layer 110 formed on the bottom surface of the core.The core may be a dielectric material, for example an epoxy-glass resinsuch as BT resin and may have a thickness of between about 40 microns(μm) to 200 μm, although the thickness of the core may vary outside ofthat range in alternative embodiments. The core may be ceramic ororganic in alternative embodiments.

The conductive layers 108 and 110 may be formed of copper or other lowresistance electrical conductor, and may be patterned as explainedhereinafter. The layers 108 and 110 may have a thickness of about 10 μmto 24 μm, although the thickness of the layers 108 and 110 may varyoutside of that range in alternative embodiments. Once patterned, thetop and bottom conductive layers may be laminated with a solder mask 112as is known in the art, and one or more gold layers may be formed onportions of the bottom conductive layer 110 to define contact fingers114 as is known in the art. Substrates including conductive layers whichmay be patterned in accordance with the present invention are availablefrom Kinsus Interconnect Technology Corp., Santa Clara, Calif.

In embodiments of the invention, substrate 100 may be patterned andconfigured for use in an LGA semiconductor package. It is understoodthat the substrate 100 and the rigid wave pattern explained hereinaftermay be used in other types of semiconductor packages, including forexample BGA packages.

FIGS. 5, 7 and 8 further show two stacked semiconductor die 116 mountedon the top surface 102 of the substrate 100 (shown in phantom in the topview of FIG. 5 and omitted from the top view of FIG. 6 for clarity).Embodiments of the invention may alternatively include a single dice,and embodiments of the invention may alternatively include between 3 and8 or more die stacked in an SiP, MCM or other type of arrangement. Theone or more die may have thicknesses ranging between 8 mils to 20 mils,but the one or more die may be thinner than 8 mils and thicker than 20mils in alternative embodiments. While not critical to the presentinvention, the one or more die 116 may be a flash memory chip(NOR/NAND), SRAM or DDT, and/or a controller chip such as an ASIC. Othersilicon chips are contemplated.

The one or more die 116 may be mounted on the top surface 102 of thesubstrate 100 in a known adhesive or eutectic die bond process, using aknown die attach compound 118. The die attach compound may be forexample any of various polymer adhesives containing conductive fillersfor electrical conductivity. Such die attach compounds are manufacturedfor example by Semiconductor Packaging Materials, Inc. of Armonk, N.Y.The one or more die 116 may be electrically connected to conductivelayers 108, 110 of the substrate 100 by wire bonds 120 in a known wirebond process.

Although not visible from the top surface of the chip carrier substrate,FIG. 5 shows a top view in phantom of the positions of contact fingers114 formed on the bottom surface 104 of the substrate 100. The contactfingers 114 are provided to establish an electrical connection in aknown manner with contact pads of a host printed circuit board (notshown), or other electronic component, when the contact fingers 114 arebrought into pressure contact against the contact pads of the hostprinted circuit board. While four contact fingers 114 are shown, it isunderstood that there may be more or less than four fingers inalternative configurations of the chip carrier substrate 100. In anembodiment, there may be eight contact fingers.

Other portions of an electrical conductance pattern may be formed on theupper and/or lower surfaces 102, 104 of the substrate in a known mannerand as explained hereinafter to provide electrical connections betweenthe one or more die 116, contact fingers 114 and/or other electroniccomponents mounted on the surfaces of substrate 100. In embodiments,aside from the rigid wave pattern and the contact fingers, there may bean electrical conductance pattern 208 (FIG. 15) on one or both surfacesof the substrate 100. In embodiments including conductance patterns onboth the top surface 102 and bottom surface 104, vias (not shown) may beprovided to transmit electrical signals between the top and bottomsurfaces of the substrate 100.

As indicated in the Background of the Invention section, for thin die,the pressure applied during the molding process often mechanicallystresses the die to the point where die cracking occurs. In order toprevent die cracking during the molding process, the present inventionemploys an etched pattern, referred to herein as a rigid wave pattern,or “RWP,” on the substrate. An embodiment of a rigid wave pattern 130 isshown in the view of the top surface 102 of substrate 100 in FIG. 6. Inembodiments of the invention, the rigid wave pattern 130 is formed onthe top surface 102 to align with and overlie the contact fingers 114formed on the opposite surface of the substrate 100. The rigid wavepattern 130 includes etched portions 132-138, and unetched portion 140surrounding the etched portions 132-138. In the configuration of thesubstrate 100 shown, there are four contact fingers 114, andaccordingly, rigid wave pattern 130 has four corresponding RWP etchedportions, one corresponding to each of the contact fingers. Inconfigurations where there are more or less contact fingers, embodimentsof the invention include correspondingly more or less RWP etchedportions. In an embodiment including eight contact fingers, there may beeight corresponding RWP etched portions. However, it is understood thatthere may be more or less RWP etched portions than there are contactfingers in alternative embodiments of the invention.

The RWP etched portions of rigid wave pattern 130 may be formed at thesame time and in the same process as the electrical conductance pattern208 on the upper surface 102. Thus, the advantages provided by thepresent invention may be achieved without any additional processingsteps or any additional fabrication costs. It is understood, however,that the rigid wave pattern may be formed of known plating materials asa separate layer on one of the layers 108 and/or 110 in alternativeembodiments. There are a number of known processes for forming the RWPetched portions. One process for forming the RWP etched portions as wellas the electrical conductance pattern 208 on the substrate 100 isexplained with reference to the flow chart of FIG. 14. The surfaces ofconductive layers 108 and 110 are cleaned in step 150. A photoresistfilm is then applied over the surfaces of layers 108 and 110 in step152. A pattern mask containing the outline of the electrical conductancepattern and rigid wave pattern is then placed over the photoresist filmin step 154. The photoresist film is exposed (step 156) and developed(step 158) to remove the photoresist from areas on the conductive layersthat are to be etched. The exposed areas are next etched away using anetchant such as ferric chloride in step 160 to define the conductanceand rigid wave patterns on the core. Next, the photoresist is removed instep 162, and the solder mask layer is applied in step 164.

In an embodiment of the present invention, each of the RWP etchedportions 132-138 has an overall width approximately equal to the widthof each of the contact fingers 114, and an overall length approximatelyequal to the length of each of the contact fingers 114. Each RWP etchedportion 132-138 includes four distinct sections, which together form aportion of an ellipse, truncated at the top and bottom, and separated atits middle between the top and bottom. Assuming a length, L (FIG. 9),parallel to the length of the contact fingers, the length L of each ofthe four distinct sections of an RWP etched portion may be approximatelyone-third the length of a contact finger. The width, W, of each sectionof an RWP etched portion may be approximately 50 μm. It is understoodthat the length, L, and width, W, may be lesser or greater than thevalues set forth above in alternative embodiments.

FIG. 9 is an enlarged view of a single RWP etched portion, for example,RWP etched portion 132. In embodiments, each of the RWP etched portions132-138 may be the same size and configuration as each other, but it isunderstood that RWP etched portions 132-138 may be sized differentlythan each other in alternative embodiments. FIG. 9 shows RWP etchedportion 132 and two rectangles in phantom. The smaller rectangle,rectangle 170, is the size of a contact finger 114, over which the RWPetched portion 132 lies on the substrate as explained hereinafter withreference to FIG. 12. The larger rectangle, rectangle 172 is therectangle having an overall width and length of an ellipse (shown inphantom) defined by the outer edges of RWP etched portion 132 (i.e., ifthe top and bottom portions of RWP etched portion 132 were nottruncated, it would form an ellipse having a width and length ofrectangle 172). In embodiments of the present invention, the rectangles170 and 172 have the same width. That is, the width of the RWP etchedportion 132 is the same as the width of the contact finger 114. Inembodiments of the present invention, rectangle 172 may range in sizefrom about the same size as rectangle 170 to a rectangle have a lengthof approximately 4.9 mm and a width of approximately 1.65 mm. It isunderstood that the size of rectangle 172 may be slightly larger orsmaller than the range set forth above in alternative embodiments.

In an embodiment of the invention, the RWP unetched portion 140surrounding each of the RWP etched portions 132-138 is generallyrectangular in shape and devoid of etching. In a first embodiment, thesize of the rectangle defined by the RWP unetched portion 140 may be assmall as a rectangle just encompassing each of the RWP etched portionstogether. In a second embodiment, the RWP unetched portion 140 mayextend in a first direction to the left edge of the conductive layer108, in a second direction to the right edge of the conductive layer108, in a third direction to a top edge of the conductive layer adjacentthe RWP etched portions, and in a fourth direction extending down to aboundary just above a circuitry pattern formed on the top surface 102 ofthe substrate 100. In further alternative embodiments, the size of theetched portion may range in size anywhere between the above-describedfirst and second embodiments. In an embodiment where there is nocircuitry on the top surface of the substrate, the RWP unetched portionmay extend down to the bottom edge of the conductive layer 108.

It is understood that the shape of RWP unetched portion 140 may be otherthan rectangular in alternative embodiments. For example, it may beoval, elliptical, circular, or some other irregular shape encompassingthe RWP etched portions.

It is also understood that the RWP etched pattern may vary from thepartial ellipse shape shown in FIGS. 6 and 9. For example, FIG. 10 showsRWP etched patterns 174-180 having straight edges, each pattern 174-180having a length and width overlying and approximately the same shape asthe contact fingers 114. The RWP etched patterns may alternatively begenerally rectangular shaped, such as RWP etched patterns 182-188 shownin FIG. 11. The center of RWP etched patterns 182-188 as shown in FIG.11 are not etched. It is understood that the centers of RWP etchedpatterns 182-188 may be etched in alternative embodiments. A furtherembodiment is shown in FIG. 12 where each of the RWP etched patterns190-196 has top and bottom lengths inclined toward each other in atriangular shape. The inclined lengths may come together at their topand bottom or may be separated from each other (as shown). A stillfurther embodiment is shown in FIG. 13 and the enlarged view of FIG. 14.RWP etched patterns 198-204 are shown including lateral thermal reliefetchings 206 extending between the lengthwise sections of the RWP etchedpattern. Thermal relief etchings may be used in embodiments to reducemechanical stresses within the layers of the substrate generated by thediffering thermal expansion coefficients of the layer 108 and core 106.The number and width of thermal relief etchings 206 across the length ofthe RWP etched patterns may vary in alternative embodiments. The thermalrelief etchings 206 may be used in any of the above-describedembodiments. It is understood that RWP etched patterns may have othershapes in alternative embodiments.

FIG. 15 is a top view of chip carrier substrate 100 including aconductance pattern 208 and a rigid wave pattern 130 according to anembodiment of the present invention. The contact fingers 114, on thebottom surface of the substrate 100, are also shown in phantom. Asshown, each of the RWP etched portions aligns with and resides over arespective contact finger 114. It is understood that the contact fingers114 may be formed at other locations on the substrate, and the rigidwave pattern moved accordingly to overlie the fingers.

With the one or more die overlying some or all of the contact fingerswhen mounted on the substrate, the rigid wave pattern according toembodiments of the present invention effectively reduces deformation ofand stresses on the individual dice, therefore substantially alleviatingdie cracking.

Moreover, while the rigid wave pattern according to embodiments ofpresent invention has been described as being positioned over thecontact fingers on opposed sides of the substrate to reduce themechanical stresses on the semiconductor dice mounted at least partiallyover the contact fingers and rigid wave pattern, it is understood thatthe rigid wave pattern may be used over other portions of theconductance pattern to reduce mechanical stresses on other components onsubstrate 100. In such embodiments, the rigid wave pattern may be formedon an opposite side of a portion of the conductance pattern, in a shapethat aligns with and compliments the portion of the conductance patternas set forth above, so as to lessen mechanical stress on a componentmounted on the substrate over the rigid wave pattern and portion of theconductance pattern.

FIG. 16 is a cross-sectional side view of a finished semiconductor diepackage 210 having substrate 100 with a rigid wave pattern and dice 116encased within molding compound 212. A process for forming the finisheddie package 210 is explained with reference to the flow chart of FIG.18. The substrate 100 starts out as a large panel which is separatedinto individual substrates after fabrication. In a step 220, the panelis drilled to provide reference holes off of which the position of therespective substrates is defined. The conductance pattern and rigid wavepattern are then formed on the respective surfaces of the panel in step222 as explained above. The patterned panel is then inspected in anautomatic optical inspection (AOI) in step 224. Once inspected, thesolder mask is applied to the panel in step 226.

After the solder mask is applied, the contact fingers are completed. Asoft gold layer is applied over certain exposed surfaces of theconductive layer on the bottom surface of the substrate, as for exampleby thin film deposition, in step 228. As the contact fingers are subjectto wear by contact with external electrical connections, a hard layer ofgold may be applied, as for example by electrical plating, in step 230.It is understood that a single layer of gold may be applied inalternative embodiments. A router then separates the panel intoindividual substrates in step 232. The individual substrates are theninspected and tested in an automated step (step 234) and in a finalvisual inspection (step 236) to check electrical operation, and forcontamination, scratches and discoloration. The substrates that passinspection are then sent through the die attach process in step 238, andthe substrate and dice are then packaged in step 240 in a knowninjection mold process to form a JEDEC standard (or other) package. Itis understood that the die package 210 including a rigid wave patternmay be formed by other processes in alternative embodiments.

The foregoing detailed description of the invention has been presentedfor purposes of illustration and description. It is not intended to beexhaustive or to limit the invention to the precise form disclosed. Manymodifications and variations are possible in light of the aboveteaching. The described embodiments were chosen in order to best explainthe principles of the invention and its practical application to therebyenable others skilled in the art to best utilize the invention invarious embodiments and with various modifications as are suited to theparticular use contemplated. It is intended that the scope of theinvention be defined by the claims appended hereto.

1. A first pattern formed of an electrical connector on a first surfaceof a substrate, the substrate capable of supporting and electricallyconnecting to a semiconductor dice, a second surface of the substrateopposite the first surface including a second pattern, the first patterncomprising: an etched portion; an unetched portion surrounding theetched portion, the first pattern for reducing a mechanical stressgenerated by the second pattern on the semiconductor dice during amolding process; wherein the etched portion of the first pattern on thefirst surface of the substrate aligns with and overlies a portion of thesecond pattern; wherein the portion of the second pattern is a contactfinger for forming an external electrical connection; and wherein theetched portion of the first pattern forms a portion of an ellipse, saidellipse having a width approximately equal to a width of the contactfinger, and said ellipse having a length greater than or equal to alength of the contact finger.
 2. A first pattern as recited in claim 1,the portion of the ellipse having a width approximately equal to a widthof the contact finger, and the portion of the ellipse having a lengthapproximately equal to a length of the contact finger.
 3. A firstpattern formed of an electrical connector on a first surface of asubstrate, the substrate capable of supporting and electricallyconnecting to a semiconductor dice, a second surface of the substrateopposite the first surface including a second pattern, the first patterncomprising: an etched portion; an unetched portion surrounding theetched portion, the first pattern for reducing a mechanical stressgenerated by the second pattern on the semiconductor dice during amolding process; wherein the etched portion of the first pattern on thefirst surface of the substrate aligns with and overlies a portion of thesecond pattern; wherein the portion of the second pattern is a contactfinger for forming an external electrical connection; and wherein theetched portion of the first pattern includes a pair of etched sectionsaligned generally along a length of the etched portion, and lateraletched sections extending laterally between the pair of etched sections.4. A rigid wave pattern formed on a first surface of a substrate, thesubstrate capable of supporting and electrically connecting to asemiconductor dice, a second surface of the substrate opposite the firstsurface including one or more contact fingers for making one or moreexternal electrical connections, the rigid wave pattern comprising: oneor more etched portions on the first surface, an etched portion of theone or more etched portions forming a portion of an elipse overlying acontact finger of the one or more contact fingers on the second surface,said ellipse having a width approximately equal to a width of thecontact finger, and said ellipse having a length greater than or equalto a length of the contact finger; and an unetched portion surroundingthe one or more etched portions, the rigid wave pattern capable ofreducing a mechanical stress generated by the contact finger on thesemiconductor dice during a molding process.
 5. The rigid wave patternas recited in claim 4, the substrate including: a core having a firstsurface and a second surface opposite the first surface; a firstconductive layer formed on the first surface of the core, the rigid wavepattern being formed in the first conductive layer; and a secondconductive layer formed on the second surface of the core, the one ormore contact fingers being formed in the second conductive layer.
 6. Therigid wave pattern as recited in claim 4, wherein the rigid wave patternis formed in a copper layer of the substrate.
 7. The rigid wave patternas recited in claim 4, wherein the unetched portion of the rigid wavepattern is rectangular in shape.
 8. A rigid wave pattern formed on afirst surface of a substrate, the substrate capable of supporting andelectrically connecting to a semiconductor dice, a second surface of thesubstrate opposite the first surface including one or more contactfingers for making one or more external electrical connections, therigid wave pattern comprising: one or more etched portions on the firstsurface, an etched portion of the one or more etched portions forming aportion of an ellipse overlying a contact finger of the one or morecontact fingers on the second surface, said ellipse having a widthapproximately equal to a width of the contact finger, and said ellipsehaving a length greater than or equal to a length of the contact finger;and an unetched portion surrounding the one or more etched portions, therigid wave pattern capable of reducing a mechanical stress generated bythe contact finger on the semiconductor dice during a molding process;said portion of the ellipse having a width approximately equal to awidth of the contact finger, and portion of the ellipse having a lengthapproximately equal to a length of the contact finger.
 9. A rigid wavepattern formed on a first surface of a substrate, the substrate capableof supporting and electrically connecting to a semiconductor dice, asecond surface of the substrate opposite the first surface including oneor more contact fingers for making one or more external electricalconnections, the rigid wave pattern comprising: one or more etchedportions on the first surface, an etched portion of the one or moreetched portions including a pair of etched sections aligned generallyalong a length of the etched portion and lateral etched sectionsextending laterally between the pair of etched sections, and overlying acontact finger of the one or more contact fingers on the second surface;and an unetched portion surrounding the one or more etched portions, therigid wave pattern capable of reducing a mechanical stress generated bythe contact finger on the semiconductor dice during a molding process.10. The rigid wave pattern as recited in claim 9, the substrateincluding: a core having a first surface and a second surface oppositethe first surface; a first conductive layer formed on the first surfaceof the core, the rigid wave pattern being formed in the first conductivelayer; and a second conductive layer formed on the second surface of thecore, the one or more contact fingers being formed in the secondconductive layer.
 11. The rigid wave pattern as recited in claim 9,wherein the rigid wave pattern is formed in a copper layer of thesubstrate.
 12. The rigid wave pattern as recited in claim 9, wherein theunetched portion of the rigid wave pattern is rectangular in shape.